The present invention relates to a discharge lamp lighting device for lighting a discharge lamp that is used as a headlight of an automobile or similar vehicle.
Among discharge lamps, such high intensity discharge lamps (HIDs) as a metal halide lamp, high pressure sodium lamp, mercury vapor lamp have been used as lights for outdoor and indoor facilities, warehouses, factories etc., and as streetlights, and so forth since they have the advantages of large luminous flux, high lamp efficiency and longevity. In recent years, they have come into use, in particular, as headlights of automobiles and the like. To light discharge lamps of this kind, a high starting voltage needs to be applied on startupxe2x80x94this necessitates the use of a lighting device provided with an igniter for generating the starting voltage as well as a stabilizer for stable lighting of the discharge lamp.
FIG. 1 is a sectional view showing the internal construction of a high-voltage generating transformer that is used as an igniter for a conventional lighting device. In FIG. 1, reference numeral 1 denotes a high-voltage generating transformer. The high-voltage generating transformer 1 is composed mainly of a columnar core disposed centrally thereof, a primary winding part 3 disposed around the core 2, a secondary winding part 4 disposed outside the primary winding part 3, and an insulator 5 for insulating the secondary winding part 3 and the primary winding part 3 from each other.
Since the high-voltage generating transformer 1 in the conventional lighting device has such a construction as mentioned above, the secondary winding part 4 for high voltage generating use is so close to the core 2 of low voltage and the periphery of the core 2 that it is necessary to put a distance of insulation L against high voltage between the core 2 and the secondary winding part 4 and between the secondary winding part 4 and the core periphery; hence, the insulator 5 of some thickness is indispensable, giving rise to a problem that the prior art transformer cannot meet the demand for miniaturization of the discharge lamp lighting device for automobiles or the like.
In the accommodation of such a request, the high-voltage generating transformer for the discharge lamp lighting device causes magnetic flux emanating from the primary winding part 3 to cross the secondary winding part 4 to generate a high voltage in the secondary winding part 4 through electromagnetic induction, and hence the transformer is required to maintain the transformer coupling property and have dielectric strength against the high voltage.
The present invention is intended to solve such problems as mentioned above, and has for its object to provide a small-size discharge lamp lighting device that permits generation of high voltage.
A discharge lamp lighting device according to an aspect of the present invention is characterized by the provision of a high-voltage generating transformer comprising a core, a secondary winding part disposed in a plurality of sections on the outside of said core, and a primary winding part disposed outside said secondary winding part, wherein a high-voltage side terminal of said secondary winding part is connected to a terminal of said core and a low-voltage side terminal of said secondary winding part is connected to a terminal of said primary winding part. With this construction, it is possible to reduce the insulation capacity in the high-voltage generating transformer and decrease the number of parts such as insulating members, achieving miniaturization of the transformer. Further, since the secondary winding part disposed on the core is divided into a plurality of sections, it is possible to suppress the potential difference between the beginning and end of the winding in each section and increase the withstand voltage of the entire secondary winding part 24 by increasing the number of winding grooves. Furthermore, since the primary winding part is disposed in the same space as that of the secondary winding divided by the respective sections of the winding grooves, it is possible to increase the power transfer efficiency from the primary winding part to the secondary winding part and hence improve the transformer coupling property. Additionally, since the primary winding part is disposed on the secondary winding part over plural sections, it is possible to cause the magnetic flux emanating from the primary winding part to cross the secondary winding part 23 over a wide range, thereby permitting generation of a high voltage from the secondary winding part through electro-magnetic induction.
A discharge lamp lighting device according to another aspect of the present invention is characterized in that the primary winding is disposed substantially uniformly all over the secondary winding part on the outside thereof. With this structure, the magnetic flux emanating from the primary winding part 24 can also be made uniform and the magnetic flux crossing the secondary winding part 24 increases, providing enhanced power transfer efficiency.
A discharge lamp lighting device according to another aspect of the present invention is characterized in that the primary winding part is formed by a high withstand-voltage electric wire. Since this enables the primary winding part to withstand a high voltage generated in the secondary winding part, the primary winding part can be disposed, without a hitch, in plural sections from the low-voltage side to the high-voltage side of the secondary winding part.
A discharge lamp lighting device according to another aspect of the present invention is characterized in that the high withstand-voltage electric wire includes a first insulating layer covering a conductor and a second insulating layer coated on the outside of said first insulating layer to ensure adhesion between a sealing resin filled outside the high withstand-voltage electric wire and said first insulating layer. This secures by the first insulating layer the high withstand voltage required of the primary winding part and ensure adhesion between the sealing resin and the first insulating layer by the second insulating layer.
A discharge lamp lighting device according to another aspect of the present invention is characterized in that said primary winding part is disposed in a low-voltage side section of said secondary winding part. This avoids the necessity for the primary winding part to have an excessive dielectric strength that the insulation of the primary winding part would be required to possess when the primary winding part is disposed in the section on the high-voltage side of the secondary winding part; hence, a thick insulation need not be provided in the primary winding part and the high-voltage generating transformer can be minimized accordingly.
A discharge lamp lighting device according to still another aspect of the present invention is characterized in that a high-voltage side of said primary winding part is placed on a high-voltage side of said secondary winding part. With this structure, it is possible to suppress the potential difference between the primary winding part and the secondary winding part on the high-voltage side to the voltage generated in the secondary winding part, providing increased margin for the withstand voltage in the insulation of the primary winding part.